The drive unit for wheel comprises a rolling-bearing unit or hub unit for supporting the wheel, a constant-velocity joint unit and a coupling member, so as to support the drive wheel {front wheel for a FF vehicle (front engine, front-wheel-drive vehicle), rear wheel for a FR vehicle (front engine, rear-wheel-drive vehicle), and any wheel for a 4WD (four-wheel-drive vehicle)} that is supported by an independent suspension rotatably with respect to the suspension, whereby the drive unit for wheel drives and rotates the drive wheel.
A hub unit or axle unit for wheel drive which can be connected and disconnected to a constant-velocity joint is called “fourth generation hub unit”.
In order to support a wheel such that it can rotate freely with respect to the suspension, various bearing units or axle units in which an outer race and inner race rotate freely by way of rolling bodies, have been used. Moreover, a rolling-bearing unit for wheel support that supports the drive wheel in an independent suspension, used together with a constant-velocity joint unit, must smoothly transmit (maintaining constant velocity) the rotation of the drive shaft to the wheel regardless relative displacement of the differential gear and drive wheel or the steering angle applied to the wheel. A bearing unit, or so called fourth-generation hub unit, which can combined in this way with a constant-velocity joint unit and which is relatively compact and lightweight, has been disclosed, for example in Japanese Patent Publication Tokukai Hei 7-317754, or U.S. Pat. No. 5,674,011.
FIG. 6 shows a first example of the prior construction as disclosed in Japanese Patent Publication Tokukai Hei 7-317754. The non-rotating outer ring 1 that is supported by the suspension, when installed in the vehicle, comprises a coupling flange 2 around the outer peripheral surface for connecting and fastening to the suspension, and a plurality of outer-ring raceways 3 formed around the inner peripheral surface thereof. On the radially inside of the outer race 1, there is a hub 6 comprising a first element 4 and second element 5. Of these, the first element 4 is formed in a cylindrical-shape on the whole such that there is an installation flange 7 formed around the outer peripheral surface on the side of the outside end (the outside end is the end on the outside in the width direction when installed in the automobile, and is the left end in the drawings of this patent), and a first inner-ring raceway 8a formed around the radially outer surface on the side of the inside end (the inside end is the end on the center side in the width direction when installed in the automobile, and is the right end in the drawings of this patent).
On the other hand, the second element 5 is formed such that there is a cylindrical section 9 on the outside end that fits radially inside the first element 4, and there is a housing section 11 on the inside end which functions as the outer ring of a Rzeppa-type or Barfield-type constant-velocity joint 10 on the bearing side, and there is a second inner-ring raceway 8b formed around its outer peripheral surface in the middle. By placing a plurality of rolling bodies 12 between the outer-ring raceways 3 and the inner-ring raceways 8a, 8b, the hub 6 is supported radially inside the outer race 1 such that it can rotate freely.
Moreover, there are a radially outside fastening groove 13 on the inner peripheral surface of the first element 4 and a radially inside fastening groove 14 on the outer peripheral surface of the second element 5 in alignment in location with each other, and by placing a retaining ring 15 in engagement with both of these fastening grooves 13, 14, the first element 4 is prevented from coming apart from the second element 5.
Furthermore, welding 17 is performed between the outer peripheral edge of one end (left end in FIG. 6) of the second element 5, and the inner peripheral edge of the stepped section 16 formed around the inner peripheral surface of the first element 4, to connect and fasten the first and second elements 4, 5.
The constant-velocity joint 10 on the bearing side comprises the housing section 11, and inner ring 18, retainer 19, and a plurality of balls 20. Of these, the inner ring 18 is fastened to the end of the drive shaft (not shown in the figure) which is driven and rotated by the engine via the transmission.
On the outer peripheral surface of this inner ring 18, there are six inside grooves 21 that have an arc-shaped cross section when cut by an imaginary plane that is orthogonal to the center axis of the inner ring 18, and these inside grooves 21 are formed at equal intervals in the circumferential direction and are orthogonal to the circumferential direction.
Also, at positions on the inner peripheral surface of the housing section 11 that face the inside grooves 21, there are six outside grooves 22 that similarly have an arc-shaped cross section, and are formed such that they run orthogonal to the circumferential direction.
In addition, the retainer 19 is formed between the outer peripheral surface of the inner ring 18 and the inner peripheral surface of the housing section 11 such that it is entirely ring shaped with an arc-shaped cross section.
At six locations in the circumferential direction around this retainer 19, there are pockets 23 at positions in alignment with the inside and outside grooves 21, 22, respectively, and there is one ball 20 held inside each of these pockets 23. These balls 20, six in total, when held in the respective pockets 23, roll freely along the inside and outside grooves 21, 22, which may be referred to as “inside engagement groove and outside engagement groove”, respectively.
When the rolling-bearing unit or axle unit for supporting the wheel constructed as described above and combined with a constant-velocity joint 10 on the bearing side, is installed in a vehicle, the outer race 1 is supported by the suspension by coupling flange 2, and the drive wheel is fastened to the first element 4 by the installation flange 7. Moreover, the end of the drive shaft or transmission shaft 53 (see FIG. 1 which shows a first embodiment of the present invention), which is rotated and driven by the engine via the transmission, is fastened inside the inner ring 18 of the constant-velocity joint 10 on the bearing side with a spline connection.
When the automobile is running, the rotation of the inner ring 18 is transmitted to the hub 6 including the second element 5 by way of the plurality of balls 20 to drive and rotate the drive wheel.
FIG. 7 shows a second example of the prior construction as disclosed in U.S. Pat. No. 5,674,011. In this second example of prior construction, an outer race 1 that does not rotate during operation is fastened inside the knuckle 24 of the suspension, and outer-ring raceways 3 are formed around its inner peripheral surface.
Around the outer peripheral surface on the outside end of the hub 6, there is an installation flange 7 for supporting the wheel, and similarly on the inside end, there is a pair of inner races 25, so that a double row of inner-ring raceways 8 is formed. Both of these inner races 25 are fastened to and supported by the main portion of the hub 6 by a crimped section 26 that is formed by bending the inside end of the hub 6 outward in the radial direction.
In addition, a plurality of rolling bodies 12 are placed between the outer-ring raceways 3 and inner-ring raceways 8, to support the hub 6 radially inside the outer race 1 such that the hub 6 can rotate freely. Moreover, there is a spline hole 27 formed in the center section of the hub 6.
Furthermore, this hub 6 is combined with the drive member 28 which may form a “second constant-velocity joint” in the present specification, such that the hub 6 can be freely rotated and driven.
On one end of this drive member 28, there is a spline shaft 29 that is engaged with the spline hole 27. Also, the other end of drive member 28 is a housing section 11 that functions as the outer ring of a Rzeppa-type or Barfield-type constant-velocity joint 10 on the bearing side.
This kind of drive member 28 and hub 6 are combined by fitting the spline shaft 29 into the spline hole 27, and are prevented from coming apart by a coupling member 30 that is made of an elastic material, which is fitted in a land and recess engagement with a first and second engagement section, which are ring-shaped grooves, that are formed on the outer peripheral surfaces of the drive member 28 and hub 6 in an interlocking manner.
Furthermore, in Japanese Patent Publication Tokukai Hei 10-264605 and U.S. Pat. No. 5,853,250, the center section of the cylindrical-shaped hub is left as is hollow without inserting the spline shaft, making it possible to reduce the weight of the rolling-bearing unit or axle unit for wheel support.
FIG. 8 shows a third example of a conventional bearing unit for driving the wheels, which is similar to those disclosed in Japanese Patent Publication Tokukai Hei 10-264605 and U.S. Pat. No. 5,853,250.
When installed in the vehicle, the outer race 1, which does not rotate when supported by the suspension, has a coupling flange 2 formed around its outer peripheral surface, for connecting to and being supported by the suspension, and a plurality of outer-ring raceways 3 formed around its inner peripheral surface.
On the radially inside of this outer race 1, there is a hollow, cylindrical shaped hub 6 that is supported such that it is concentric with the outer race 1. This hub 6 has an installation flange 7 formed around its outer peripheral surface near the outside end for supporting the wheel, and similarly there is a first or outside inner-ring raceway 8a formed around the center section.
Moreover, there is a small-diameter step section 31 formed around the outer peripheral surface near the inside end of the hub 6, and an inner race 25, with a second or inside inner-ring raceway 8b formed on the inside around its outer surface, fits around and is fastened to the small-diameter step section 31.
In addition, rolling bodies 12 are placed between the outer-ring raceways 3 and inner-ring raceways 8a, 8b such that they can roll freely, and they support the hub 6 radially inside the outer race 1 such that it rotates freely.
Also, there are seal rings 32 placed between the inner peripheral surface on both ends of the outer race 1 and the outer peripheral surface of the middle section of the hub 6 and the outer peripheral surface on the inside end of the inner race 25, and they seal the openings on both ends of the space where the rolling bodies 12 are located.
On the inside end of the hub 6 there is a housing section 11 that functions as the outer ring of the Rzeppa-type or Barfield-type constant-velocity joint 10 (which can be referred to as “second constant velocity joint in this specification) on the bearing side, and it is connected to the hub 6 by way of an auxiliary ring 33 (which can function as a spacer).
On the inner and outer peripheral surfaces of this short, cylindrical shaped auxiliary ring 33, a radially inner female spline section 34 is formed on the inner peripheral surface, and a radially outer male spline section 35 is formed on the outer peripheral surface. This kind of auxiliary ring 33 is connected to the outer peripheral surface on the inside end of the hub 6 such that the radially inner male spline section 36 on the outer peripheral surface thereof and radially inner female spline section 34 are engaged with each other through a spline connection with no backlash.
Moreover, in this condition, the inside end of the auxiliary ring 33 is held by the crimped section 26 formed on the inside end of the hub 6, so that the auxiliary ring 33 is fastened to the inside end of the hub 6 with no backlash.
On the other hand, the radially outer female spline section 37 that is formed on the inner peripheral surface on the outside end of the housing section 11 is engaged through a spline connection with the radially outer male spline section 35 that is formed on the outer peripheral surface of the auxiliary ring 33.
Moreover, a plurality of outside grooves 22 for engagement are formed around the inner peripheral surface on the inside half portion of the housing 11, such that they function as the raceways for the balls 20 of the Rzeppa-type or Barfield-type constant-velocity joint 10 on the bearing side. In addition, an radially outer female spline section 37 is formed on the inner peripheral surface on the outside end. In this way, the radially outer female spline section 37 is connected with a spline fit with the radially outer male spline section 35 that is formed on the outer peripheral surface of the auxiliary ring 33.
Between the radially outer female spline section 37 and the radially outer male spline section 35 that are connected by a spline fit, there is a coupling member or retaining ring 15a, such that the housing section 11 and the auxiliary ring 33 are not separated. In other words, the retaining ring 15a formed in an open ring shape is located between and engaged with a first fitting section or inside fitting groove 14a that is formed around the entire outer peripheral surface of the auxiliary ring 33, and a second fitting section or outside fitting groove 13a that is formed around the entire inner peripheral surface on the end of the housing 11, such that the housing section 11 and auxiliary ring 33 do not shift or move in the axial direction. Moreover, a cap 38 made of pressed sheet steel is fitted and fastened to the inner peripheral surface in the middle section of the housing section 11 such that it blocks between the space where the plurality of balls 20 are located and the interior space of the hub 6 which runs to the outside in the axial direction.
In the case of the first example of prior construction shown in FIG. 6, the transmission of rotation between the first and second elements 4, 5 of the hub 6 must be performed in the section of the weld 17. In other words, it is necessary to transmit large torque for driving between the first element 4, which supports the wheel, and the second element 5, which is connected to the drive shaft, however, since the cylindrical surfaces of these elements 4, 5 fit together, it is not possible to transmit large torque through these fitting cylindrical surfaces.
Accordingly, it is necessary large torque be transmitted in the section of the weld 17, so that it is necessary that the strength of this weld section 17 is sufficiently large and thus this weld section must be welded using build-up welding all the way around.
However, when this weld section 17 is welded using build-up welding all the way around, the heat during welding causes the shape of the inner-ring raceway 8a, which is formed on the outer peripheral surface of the first element 4, to deform, and as a result the hardness of the section of this inner-ring raceway 8 decreases and it becomes impossible to sufficiently maintain the durability of the bearing unit which includes this inner-ring raceway 8a. 
On the other hand, in both the second and third examples of prior construction shown FIG. 7 and FIG. 8, torque is transmitted from the constant-velocity joint 10 on the bearing side to the hub 6 by way of the spline connection. The term “spline connection or fit” is used to include the serrated connection or fit section, which has a finer pitch than the spline in this specification.
In other words, in the case of the second example of prior construction shown in FIG. 7, torque is transmitted by the spline connection between the female spline section formed on the inner peripheral surface of the spline hole 27, and the male spline section formed on the outer peripheral surface of the spline shaft 29, and in the case of the third example of prior construction shown in FIG. 8, the torque is transmitted by the spline connection between the radially outer male spline section 35 that is formed on the outer perineal surface of the auxiliary ring 33 and the radially outer female spline section 37 that is formed on the inner peripheral surface on the outside end of the housing section 11.
In the case of this construction for transmitting the torque by the spline connection, although there is not the problem that existed in the first example of prior construction shown in FIG. 6, the specifications of the spline connection section must be accurately regulated, otherwise installation of this spline connection would become troublesome and abnormal noise could occur during operation which would give discomfort to the passengers of the vehicle.
In other words, when making the fit between the female spline section and male spline section of the spline connection by way of interference fit, the work of fitting these spline sections together becomes troublesome, large assembly equipment is necessary and efficiency of the assembly work is decreased.
On the other hand, when there is an excessively loose fit between the female spline section and male spline section, there is a large clearance between the side surfaces in the circumferential direction of the spline teeth of both of these spline sections, so during acceleration or deceleration, these side surfaces in the circumferential direction hit each other with large momentum and may cause noise that could cause discomfort to the passengers of the vehicle.